The present invention relates to a portable apparatus including an acoustic signal generation device.
A portable apparatus can be, for example, a portable cordless telephone operating in a digital telecommunication system of the DECT type or in a mobile radiocommunication system of the GSM type.
The Japanese patent specification no. 9101786A describes a portable cordless telephone including an acoustic signal generation device by means of which melodies can be generated with the aid of a digital signal processor although only minimal memory means are used. The melody generation device has a data memory which stores the data relating to the melody such as the notes. A controller sequentially reads out the data relating to the notes. A sound generator produces a periodic source signal having the frequency of the note. An envelope generator produces an envelope signal which is combined with the source signal in order to generate the melody.
The prior-art device for generating the acoustic signal has the drawback that it generates a melody of poor musical sonority, which is therefore not pleasant to listen to for the user.
It is an object of the invention to remedy this drawback by proposing a portable apparatus having an acoustic signal generation device producing a pleasant sound.
To this end, the present invention proposes a portable apparatus including an acoustic signal generation device comprising:
an input unit for supplying a digital input signal,
a delay line for initially receiving N samples of the digital input signal, the value N being dependent on the fundamental frequency of the acoustic signal to be produced, for storing and delaying data values associated with the samples,
an arithmetic unit for combining at least two delayed data values received from the delay line in order to form a modified data value, which is again stored in the delay line and delayed by the period N, the modified data values together also forming an output signal,
an output unit for producing the acoustic signal on the basis of said output signal.
Such an acoustic signal generation device enables the frequency content of digital input signal initially fed into the delay line to be modified in a simple manner owing to the arithmetic unit. The sound timbre obtained at the output of the acoustic signal generation device is found to be richer as a result of the presence of harmonics in addition to the fundamental frequency of the acoustic signal. The portable apparatus including such a device thus enables the generation of melodies which are more pleasant to listen to, the sounds produced being closer to natural sounds, in contradistinction to conventional portable apparatuses, which generate sounds of musically poor quality based on sinusoidal signals.
The present invention also proposes a portable apparatus including an acoustic signal generation device comprising:
up-sampling means for computing an up-sampling frequency on the basis of the fundamental frequency of the acoustic signal to be produced, of a sampling frequency at which the output signal should be supplied, and of a maximum length of the delay line, the data being processed by the delay line and the arithmetic unit at the up-sampling frequency thus determined,
down-sampling means for down-sampling the output signal sampled at the up-sampling frequency in order to supply an output signal sampled at the sampling frequency to the output unit.
By means of such a device it is possible to optimize the content of the delay line and, as a consequence, the processing of the digital input signal by the delay line in conjunction with the arithmetic unit as a function of the fundamental frequency of the acoustic signal to be generated.